Light emitting device

ABSTRACT

A light emitting device includes a light emitting element adapted to emit blue light, quantum dots that absorb part of the blue light emitted from the light emitting element to emit green light, and at least one of a KSF phosphor adapted to absorb part of the blue light emitted from the light emitting element to emit red light and a MGF phosphor adapted to absorb part of the blue light emitted from the light emitting element to emit red light.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This is a continuation application of U.S. patent application Ser. No.16/059,709, filed Aug. 9, 2018, which is a continuation application ofU.S. patent application Ser. No. 14/859,980, filed Sep. 21, 2015 whichclaims priority to Japanese Patent Application 2014-193509 filed on Sep.24, 2014, the disclosure of which is incorporated herein by reference inits entirety.

BACKGROUND Technical Field

The present invention relates to light emitting devices, and moreparticularly to a light emitting device which includes a light emittingelement that emits a blue light, and quantum dots that emit a greenlight by absorbing part of the blue light emitted from the lightemitting element.

Description of the Related Art

Conventionally, light emitting devices that emit white light are known.This type of light emitting device includes a light emitting elementthat emits a blue light, a green phosphor that emits a green light (or ayellow-green phosphor that emits a yellow-green light) by absorbing partof the blue light emitted from the light emitting element, and a redphosphor that emits a red light by absorbing part of the blue lightemitted from the light emitting element. Such a light emitting devicethat emits a white light is used for various applications, includingillumination devices and backlights for various displays, such as aliquid crystal display.

In recent years, light emitting devices having all or part of thephosphor replaced by quantum dots (QDs) have been developed. A quantumdot is a semiconductor particle having a diameter of several nanometersto tens of nanometers, and can absorb light such as a blue light emittedfrom a light emitting element and emit a light different from theabsorbed light, as seen in a phosphor. A light emitting device whichincludes green quantum dots to absorb a blue light emitted from a lightemitting element to emit a green light and red quantum dots to absorb ablue light emitted from the light emitting element to emit a red lightis also known. For example, JP 2008-544553 A discloses a light emittingdevice that includes a yellow-green phosphor and red quantum dots.

The quantum dot features a sharp emission peak, that is, a small(narrow) full width at half maximum of the emission peak. Thus, thelight emitting device using the quantum dots has an advantage of a widecolor reproducibility range when combined with a color filter of aliquid crystal display or the like. Further, matching the peakwavelength of the color filter (a wavelength at which its transmittancereaches a peak) to the emission peak of the quantum dots allow for morelight to pass through the color filter, which improves the lightextraction efficiency with less attenuation of the light in use of thecolor filter. In particular, conventional green phosphors andyellow-green phosphors have the respective broad emission peaks. Thus,by use of the green quantum dots, these effects can be remarkablyexhibited.

However, these conventional light emitting devices employing the quantumdots are designed to use red quantum dots and may lead to the occurrenceof secondary absorption. That is, the red quantum dots may absorb partof green, or yellow-green, light emitted from green quantum dots or agreen, or yellow-green, phosphor that has absorbed the blue light, andthen emit a red light. The occurrence of such secondary absorption leadsto a reduction in the luminous efficiency of the whole light emittingdevice. Further, in many applications such as displays and illuminationdevices, there has arisen a need for a light emitting device that canemit brighter light with lower power consumption, that is, which hashigh luminance efficiency.

SUMMARY

It is an object of the present invention to provide a light emittingdevice that achieves the high luminous efficiency while utilizingquantum dots, especially, green quantum dots.

According to embodiments of the present invention, a light emittingdevice comprises a light emitting element adapted to emit blue light; aplurality of quantum dots adapted to absorb a portion of the blue lightemitted from the light emitting element to emit green light; and atleast one of a KSF phosphor and a MGF phosphor, wherein the KSF phosphoris a compound having the chemical formula A₂[M_(1−a)Mn⁴⁺ _(a)F₆] (1),where A is at least one selected from the group consisting of K⁺, Li⁺,Na⁺, Rb⁺, Cs⁺, and NH⁴⁺, M is at least one element selected from thegroup consisting of Group 4 elements and Group 14 elements, and 0<a<0.2;and the KSF phosphor is adapted to absorb at least a portion of the bluelight emitted from the light emitting element to emit red light; whereinthe MGF phosphor is a compound having the chemical formula(x−a)MgO.(a/2)Sc₂O₃.yMgF₂.cCaF₂·(1−b)GeO₂.(b/2)Mt₂O₃:zMn⁴⁺ (2), where2.0≤x≤4.0, 0<y<1.5, 0<z<0.05, 0≤a<0.5, 0<b<0.5, 0≤c<1.5, y+c<1.5, and Mtis at least one element selected from Al, Ga and In; and the MGFphosphor is adapted to absorb at least a portion of the blue lightemitted from the light emitting element to emit red light.

In an embodiment, a liquid crystal display device, comprises a lightemitting element device, wherein the light emitting device comprises alight emitting element adapted to emit blue light, the light emittingelement disposed on a surface of a light emitting element package; asealing resin covering the light emitting element, the sealing resinincluding at least one of a KSF phosphor and a MGF phosphor, wherein theKSF phosphor and a MGF phosphor are adapted to absorb at least a portionof the blue light emitted from the light emitting element to emit redline; and a plurality of quantum dots adapted to absorb a portion of theblue light emitted from the light emitting element to emit green light;a light guide plate having an upper and lower surface, the light guideplate disposed between the sealing resin and the light emitting elementpackage; a reflective plate disposed facing the lower surface of thelight guide plate; a quantum dot layer disposed facing the upper surfaceof the light guide plate, the quantum dot layer including the pluralityof quantum dots; a lower polarizing film disposed on the quantum dotlayer; a liquid crystal cell disposed on the lower polarizing film; acolor filter array disposed on the liquid crystal cell; and an upperpolarizing film disposed on the color filter array.

Embodiments of the present invention may be more fully understood fromthe description of the preferred embodiments as set forth below,together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross-sectional view of a light emitting device100 according to a first embodiment.

FIG. 2 shows preferable chromaticity ranges for light emitted from alight emitting element package 10 on chromaticity coordinate.

FIG. 3A shows a SEM image of a cross section of part of a thus obtainedlight emitting element package 10.

FIG. 3B shows an enlarged SEM image of portion A shown in FIG. 3A.

FIG. 3C shows an enlarged SEM image of portion B shown in FIG. 3A.

FIG. 3D shows an enlarged SEM image of portion C shown in FIG. 3A.

FIG. 3E shows an enlarged SEM image of portion D shown in FIG. 3B.

FIG. 4 shows an emission spectrum of the thus obtained light emittingelement package 10.

FIG. 5 shows a schematic cross-sectional view of a light emitting device100A according to a second embodiment.

FIG. 6A is an exemplary cross-sectional view illustrating the advantagesof the light emitting device 100, showing an embodiment of red phosphorparticles 14 disposed in a sealing resin 12.

FIG. 6B is an exemplary cross-sectional view illustrating the advantagesof the light emitting device 100A, showing an embodiment of red phosphorparticles 14 disposed in a light-transmissive material 22.

FIG. 7 is a schematic cross-sectional view showing a liquid crystaldisplay device 200 that has a light emitting device 100B according to athird embodiment.

DETAILED DESCRIPTION

In the following, embodiments of the present invention will be describedwith reference to the accompanying drawings. It is understood that theembodiments described below are to embody the technical concept of thepresent invention, and not intended to limit the scope of the presentinvention. The arrangements mentioned in one embodiment can also beapplied to other embodiments, unless otherwise specified. In thedescription below, if necessary, the terms indicative of the specificdirection or position (for example, “upper”, “lower”, “right”, “left”,and other words including these words) are used for easy understandingof the present invention with reference to the figures. The meanings ofthe terms are not intended to restrict the technical range of thepresent invention.

It is understood that in some drawings, the sizes or positionalrelationships of members are emphasized to clarify the description belowand are not limiting. The same parts or members are designated by thesame reference character throughout the drawings. Further, a memberdenoted by a combination of a numerical number and a letter, forexample, a reference character “10A”, may have the same structure asthat of a member denoted by the same numerical number without anyletter, for example, a reference character “10”, or that of a memberdenoted by a combination of the same numerical number and a differentletter unless otherwise specified.

As a result of intensive studies, the inventors have discovered thatwhen used in place of the red quantum dots, at least one of a KSFphosphor and a MGF phosphor as the red phosphor allows for obtaininghigh luminous efficiency in the light emitting device that employs thegreen quantum dots. The KSF phosphors and the MGF phosphors to bedescribed in detail below absorb blue light emitted from the lightemitting element and emit red light, and absorb little green lightemitted from the green quantum dots. That is, the secondary absorptionis reduced or does not occur. Thus, the light emitting devices accordingto the embodiments of the present invention have high luminousefficiency. The peak of the emission spectrum of each of the KSFphosphors and the MGF phosphors has a narrow full width at half maximumof about 10 to 20 nm. Accordingly, red light having a narrow full widthat half maximum can be obtained even through a color filter that allowsthe light in the substantially whole red wavelength range to passtherethrough, so that red light of high color purity can be obtained.

The term “quantum dot” in the present specification refers to awavelength converting material using a quantum size effect of ultrafinesemiconductor particles (semiconductor nanoparticles). It is known thatthe ultrafine particles of semiconductor having a particle size of,e.g., tens of nanometers or less, exhibit a quantum size effect.

The term “quantum size effect” refers to a phenomenon that therespective bands of a valence band and a conduction band, which arecontinuous in bulk particles, become discrete with the particle size ofthe order of nano-meters, and a band gap energy varies depending on theparticle size. Such semiconductor nanoparticles that exhibit the quantumsize effect absorb light and emit light corresponding to the band gapenergies, and thus can be used as the wavelength converting material inthe light emitting devices.

Light emitting devices according to multiple embodiments of the presentinvention will be described below in detail.

1. First Embodiment

FIG. 1 shows a schematic cross-sectional view of a light emitting device100 according to a first embodiment. The light emitting device 100includes a light emitting element 1 adapted to emit a blue light, greenquantum dots 24 to absorb a portion of the blue light emitted from thelight emitting element 1 to emit a green light, and particles of a redphosphor 14 to absorb a portion of the blue light emitted from the lightemitting element 1 to emit a red light. The red phosphor 14 is at leastone of a KSF phosphor and a MGF phosphor, discussed in detail below.

In the light emitting device according to embodiments of the presentinvention, the positional relationships between the red phosphorparticles 14 and the green quantum dots 24 with respect to the lightemitting element 1 is not specifically limited. For example, the redphosphor particles 14 may be arranged closer than the green quantum dots24. Alternatively, the red phosphor particles 14 may be arranged fartherthan the green quantum dots 24. Further, in an embodiment that will bedescribed below, the red phosphor particles 14 and the green quantumdots 24 may be arranged at approximately same distance from the lightemitting element 1. In the first embodiment, the red phosphor particles14 are arranged closer than the green quantum dots 24.

The light emitting device 100 includes a light emitting element package10. The light emitting element package 10 includes a resin package 3having a bottom surface and sidewalls that define a cavity openingupward, a light emitting element 1 disposed on the bottom surface in thecavity of the resin package 3, and a sealing resin 12 filled in thecavity of the resin package 3. The light emitting element 1 has itspositive electrode and negative electrode connected to an external powersource via conductive members, such as a metal wire, a metal bump or aplated member. Upon being supplied with electric current (electricpower) from the external power source, the light emitting element 1emits a blue light.

A lead may be disposed at the bottom surface in the cavity of the resinpackage 3, and the light emitting element 1 may be disposed on the lead.The lead may be connected to the negative electrode and/or the positiveelectrode by a metal wire, to connect the light emitting element 1 tothe external power source via the lead. Instead of using the metal wire,flip-chip bonding can be formed with the use of a solder. The lead mayhave a plated layer on its surface as needed.

The sealing resin 12 covers the light emitting element 1. As shown inthe embodiment illustrated in FIG. 1 , the sealing resin 12 covers theupper surface and the side surfaces of the light emitting element 1except for its bottom surface.

The sealing resin 12 contains the red phosphor 14, and the red phosphorparticles 14 are distributed substantially evenly in the sealing rein12. Note that although in the embodiment shown in FIG. 1 , the redphosphor particles 14 are substantially uniformly dispersed in thesealing resin 12, the distribution of the red phosphor particles is notlimited thereto. Alternatively, the red phosphor particles 14 may bedisposed at a higher density in a portion of the sealing resin 12. Forexample, the red phosphor particles 14 may be disposed at a high densitynear the light emitting element 1. One example of such an arrangementmay be called a “sedimentation arrangement,” in which the distributiondensity of the red phosphor particles is smaller at an upper part of thesealing resin 12 and higher at the bottom of the sealing resin 12(including a portion directly above the light emitting element 1). Thesedimentation arrangement can be formed, for example, by filling uncuredsealing resin 12 with the red phosphor particles 14 uniformlydistributed therein into the cavity of the resin package 3, standing thesealing resin 12 for a predetermined time while keeping it in theuncured state, allowing the red phosphor particles 14 in the sealingresin 12 to be gravitationally guided, and after the density of the redphosphor particles becomes high at the bottom of the sealing resin 12,then, hardening the sealing resin 12. Alternatively, the red phosphorsmay be settled out by a centrifugal force. In addition to the redphosphors 14, fillers may be distributed in the sealing resin 12.

The light emitting element package 10 has its upper surface serving asan emission surface and is configured to emit a blue light and a redlight. A portion of the blue light emitted from the light emittingelement 1 passes through the sealing resin 12 and is emitted from theupper surface of the sealing resin 12 to the outside. A portion of theblue light emitted from the light emitting element package 10 may bereflected at a side surface and/or the bottom surface of the resinpackage 3 while propagating inside the sealing resin 12, and then beemitted from the upper surface of the sealing resin 12. Another portionof the blue light emitted from the light emitting element 1 may beabsorbed in the red phosphor particles 14 while propagating through thesealing resin 12, whereby the red phosphor particles 14 are excited toemit a red light. The red light emitted from the red phosphor particles14 passes through the sealing resin 12 and is emitted from the uppersurface of the sealing resin 12 toward the outside. A portion of the redlight emitted from the red phosphor particles 14 is reflected at theside surfaces and/or the bottom surface of the resin package 3 whilepropagating through the sealing resin 12, and then is emitted from theupper surface of the sealing resin 12.

A green quantum dot-containing layer 20 is disposed outside the sealingresin 12, that is, in FIG. 1 , over the sealing resin 12 (or resinpackage 3) in FIG. 1 . The green quantum dot-containing layer 20includes a light-transmissive material 22 and the green quantum dots 24.That is, the green quantum dots 24 are distributed in thelight-transmissive material 22. The green quantum dot-containing layer20 may have any form. One preferable form of the green quantumdot-containing layer 20 is a sheet shape (or film shape) as shown inFIG. 1 . This is because the thickness of the green quantumdot-containing layer 20 can be made uniform to suppress colorunevenness.

With this arrangement, in the light emitting device 100, the redphosphors 14 are positioned closer to the light emitting element 1 thanthe green quantum dots 24. The KSF phosphors or MGF phosphors having alarge particle size (or diameter) of, e.g., 20 to 50 μm are disposedcloser to the light emitting element, while the green quantum dots 24having a particle size (or diameter) of, e.g., 2 to 10 nm are disposednear the light emitting element 1. Such an arrangement may suppress thescattering of light, including the scattering of green light due to thepresence of the red phosphors 14, resulting in further improving thelight extraction efficiency (that is, luminous efficiency). Theimprovement of the light extraction efficiency will be described indetail below after description of the structure of the following secondembodiment.

A large portion of the red light emitted from the upper surface of thelight emitting element package 10 propagates into the green quantumdot-containing layer 20 from its lower surface, passes through thelight-transmissive material 22 of the green quantum dot-containing layer20, and then exits from the upper surface of the green quantumdot-containing layer 20 to the outside.

A large portion of the blue light emitted from the upper surface of thelight emitting element package 10 enters the green quantumdot-containing layer 20 from its lower surface. A portion of the bluelight that has entered the green quantum dot-containing layer 20 fromthe lower surface passes through the light-transmissive material 22 ofthe green quantum dot-containing layer 20, and then exits from the uppersurface of the green quantum dot-containing layer 20 to the outside.Another portion of the blue light that has entered the green quantumdot-containing layer 20 from its lower surface is partially absorbed inthe green quantum dots 24, whereby the green quantum dots 24 emit greenlight. A large portion of the green light emitted from the green quantumdots 24 propagates through the light-transmissive material 22 and thenexits from the upper surface of the green quantum dot-containing layer20 to the outside. As a result, a white light that is a mixture of theblue light, the red light, and the green light can be obtained outsidethe upper surface of the green quantum dot-containing layer 20.

Note that a portion of the green light emitted from the green quantumdots 24 propagates downward and exits from the lower surface of thegreen quantum dot-containing layer 20, and then enters the sealing resin12 from the upper surface of the light emitting element package 10.However, the red phosphor 14, which is at least one of a KSF phosphorand a MGF phosphor, hardly absorb the green light. Accordingly, aportion of green light emitted from the upper surface of the greenquantum dot-containing layer 20 may be the light, for example, that isreflected at the inner surface of the resin package 3 and emitted fromthe upper surface of the light emitting element package 10, then entersthe green quantum dot-containing layer 20 from its lower surface andthen is emitted from the upper surface of the green quantumdot-containing layer 20. The presence of such green light contributes toimproving the light extraction efficiency of the light emitting device100.

In the embodiment shown in FIG. 1 , the green quantum dot-containinglayer 20 and the sealing resin 12 (or resin package 3) are spaced apartfrom each other. Thus, the light emitting device can have the effect ofsuppressing the transfer of heat generated from the light emittingelement 1 to the green quantum dots 24, which are sensitive to heat.

The arrangement, however, is not limited thereto, and alternatively, thegreen quantum dot-containing layer 20 and the sealing resin 12 (or resinpackage 3) may be in contact with each other. In this embodiment, alarger amount of light emitted from the light emitting element package10 is allowed to enter the green quantum dot-containing layer 20, sothat the light extraction efficiency can be further improved. Moreover,even in an embodiment where the green quantum dot-containing layer 20 isin contact with the sealing resin 12 (or resin package 3), the lightemitting element 1 is spaced apart from the green quantum dots 24 tosome degree, so that thermal degradation of the green quantum dots 24can be suppressed.

In the embodiment shown in FIG. 1 , the light emitting element package10 is a top-view type package in which the mounting surface is thebottom surface (lower surface); that is, the mounting surface is at theopposite side to the light extraction surface (for example, the uppersurface serves as the light extraction surface and the lower surfaceserves as the mounting surface). However, the light emitting elementpackage 10 is not limited thereto, and the light emitting elementpackage 10 may be structured as a so-called side view type, in which asurface adjacent to the light extraction surface serves as the mountingsurface.

In the embodiment shown in FIG. 1 , the light emitting element package10 that includes the resin package 3 is used, but is not limitedthereto. In another embodiment, a “packageless type” may be employed inplace of the light emitting element package 10, in which a phosphorlayer containing the red phosphor particles 14 is formed on the surfaceof the light emitting element 1 without having a resin package.

FIG. 2 is a diagram showing preferable chromaticity ranges of the lightemitted from embodiments of the light emitting element package 10 (i.e.the light entering the green quantum dot-containing layer 20) onchromaticity coordinates. The chromaticity of light emitted from thelight emitting element package 10 is preferably in a quadrangular regionindicated by dashed lines in FIG. 2 (i.e. a quadrangular region formedby connecting four points of (0.4066, 0.1532), (0.3858, 0.1848),(0.1866, 0.0983) and (0.1706, 0.0157) on xy chromaticity coordinatesystem of CIE1931 chromaticity diagram).

The chromaticity of light emitted from the light emitting elementpackage 10 is more preferably in a quadrangular region indicated bysolid lines in FIG. 2 (i.e. a quadrangular region formed by connectingfour points of (0.19, 0.0997), (0.19, 0.027013), (0.3, 0.09111) and(0.3, 0.014753) on xy chromaticity coordinate system of CIE1931chromaticity diagram).

With the chromaticity within such regions, under the presence of thegreen quantum dot-containing layer 20, a color tone suitable for backlight can be achieved.

A light emitting element package 10 to emit light of the chromaticitywithin those regions were prepared and the emission spectrum weremeasured, as described below.

FIG. 3A shows a SEM image of a cross section of a portion of the lightemitting element package 10. FIG. 3B shows an enlarged SEM image of theportion A shown in FIG. 3A. FIG. 3C shows an enlarged SEM image of theportion B shown in FIG. 3A. FIG. 3D shows an enlarged SEM image of theportion C shown in FIG. 3A, and FIG. 3E shows an enlarged SEM image ofthe portion D shown in FIG. 3B.

A resin package 3 was provided with a cavity defined in a substantiallysquare shape with rounded corners in the top view, with an outsidedimensions of 4 mm in length, 1.4 mm in width and 0.6 mm in height. Theresin package 3 was provided with a pair of leads 5 on the bottom in thecavity, and each of the leads 5 had a plated layer on its surfaces. Alight emitting element 1 having a light-transmissive substrate 13 and asemiconductor layer 11 was disposed on one of the pair of leads 5. Thelight emitting element 1 was electrically connected to the pair of leads5 by gold wires, respectively. The light emitted from the light emittingelement 1 has a peak of emission intensity between 435 nm and 465 nm.

The sealing resin 12 was disposed such that a silicon resin having thered phosphor particles 14 and the filler particles 15 distributedtherein was disposed in the cavity of the resin package 3, and then, thered phosphor particles 14 and the filler particles 15 were centrifugallysedimented to form a sealing resin 12. For the red phosphor 14, a KSFphosphor (K₂MnF₆:Mn⁴⁺) was used. For the filler 16, a silica filler anda nanosilica filler were used. The sealing resin 12 contained about 17parts by weight of a KSF phosphor, about 5 parts by weight of a silicafiller and about 0.4 parts by weight of a nanosilica filler with respectto 100 parts by weight of the silicone resin. As shown in FIG. 3C, anupper portion of a side surface of the light emitting element 1 wascovered with neither the red phosphor 14 nor the filler 15.

FIG. 4 shows an emission spectrum of the light emitting element package10 thus obtained. The light emitting element 1 emits light of awavelength mainly between 430 nm and 480, and the red phosphor 14 emitslight of a wavelength mainly between 600 nm and 660. The emissionspectrum has a first peak wavelength at 447 nm at which the highestemission intensity is obtained, and a second peak wavelength at 631 nmat which the highest emission intensity of the red phosphor 14 isobtained. The ratio of the emission intensity at the first wavelength ofthe emission peak to the emission intensity at the second wavelength ofthe emission peak is 100:67 (i.e. the first emission intensity:thesecond emission intensity=100:67). The values of chromaticitycoordinates in the CIE 1931 system were x=0.216 and y=0.054.

Next, the respective elements of the light emitting device 100 will bedescribed in detail.

1) Light Emitting Element

The light emitting element 1 may be of any appropriate known lightemitting element or blue LED chip, as long as it can emit a blue light(with the emission peak wavelength in a range of 435 to 465 nm). Thelight emitting element 1 may include a semiconductor stacked-layer body,and preferably includes a nitride semiconductor stacked-layer body. Thesemiconductor stacked-layer body (preferably, nitride semiconductorstacked-layer body) may include a first semiconductor layer (forexample, an n-type semiconductor layer), an emission layer, and a secondsemiconductor layer (for example, a p-type semiconductor layer) in thisorder. For example, In_(X)Al_(Y)Ga_(1−X−Y)N (0≤X, 0≤Y, X+Y≤1) may besuitably used for a nitride semiconductor material. The thickness andthe layer structure of each layer may be determined in a manner known tothose skilled in the art.

2) Red Phosphor

The red phosphor 14 is at least one of a KSF phosphor and a MGFphosphor. The KSF phosphors and the MGF phosphors hardly absorb greenlight, and thus are advantageous that secondary absorption hardlyoccurs. The red phosphors have a half-width of the emission peak of 35nm or less, and preferably 10 nm or less. The KSF phosphors and the MGFphosphors will be described in detail below.

(KSF Phosphors)

The KSF phosphors are a red phosphor having the wavelength of theemission peak in a range of 610 to 650 nm. The composition of the KSFphosphors is represented by the following chemical formula (1):A₂[M_(1−a)M⁴⁺ _(a)F₆]  (1)where A is at least one selected from the group consisting of K⁺, Li⁺,Na⁺, Rb⁺, Cs⁺ and NH⁴⁺; M is at least one element selected from thegroup consisting of Group 4 elements and Group 14 elements; and asatisfies an inequality expression of 0<a<0.2.

The full width at half maximum of the emission peak of the KSF phosphoris 10 nm or less. Examples of KSF phosphors are disclosed by JapanesePatent Application No. 2014-122887 and U.S. Pat. No. 9,120,972, filed bythe applicant of the present application. The entire contents ofJapanese Patent Application No. 2014-122887 and U.S. Pat. No. 9,120,972are incorporated herein by reference.

One embodiment of a method of manufacturing a KSF phosphor will bedescribed below. First, KHF₂ and K₂MnF₆ are weighed to attain a desiredcomposition ratio. The weighed KHF₂ is dissolved in an HF aqueoussolution thereby preparing a solution A. The weighed K₂MnF₆ is dissolvedin the HF aqueous solution, thereby preparing a solution B. Further, anaqueous solution containing H₂SiF₆ is prepared to attain a desiredcomposition ratio, producing a solution C containing the H₂SiF₆. Each ofthe solutions B and C is dripped into the solution A while stirring thesolution A at room temperature. The solution containing the thusobtained precipitate is subjected to solid-liquid separation, washedwith ethanol, and then dried to produce a KSF phosphor.

(MGF Phosphor)

The MGF phosphors are a red phosphor that emits a deep-red fluorescence.That is, the MGF phosphors are activated with Mn⁴⁺ and have a wavelengthof the emission peak of 650 nm or more, which is located at a longerwavelength side than the peak emission wavelength of the KSF phosphors.One example of the composition of the MGF phosphors is represented bythe following chemical formula: 3.5MgO.0.5MgF₂.GeO₂:Mn⁴⁺ The MGFphosphors have a full width at half maximum of 15 nm to 35 nm.

In the MGF phosphors, Mg in MgO in the composition may be partiallysubstituted by another element, such as Li, Na, K, Sc, Y, La, Ce, Pr,Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, V, Nb, Ta, Cr, Mo, W, orthe like, and/or the Ge in GeO₂ may be partially substituted by anotherelement, such as B, Al, Ga, In, or the like, in order to improve theluminous efficiency. It is preferable that substituting Mg and Ge by Scand Ga, respectively, can further improve the emission intensity oflight in a wavelength range of 600 to 670 nm, which is called a deepred.

The MGF phosphors are represented by the following chemical formula (2):(x−a)MgO.(a/2)Sc₂O₃ .yMgF₂ .cCaF₂.(1−b)GeO₂.(b/2)Mt₂O₃ :zMn⁴⁺  (2)where x, y, z, a, b, and c satisfy the following inequality expressions:2.0≤x≤4.0, 0<y<1.5, 0<z<0.05, 0≤a<0.5, 0<b<0.5, 0≤c<1.5 and y+c<1.5, andMt is at least one kind of element selected from Al, Ga and In.

In the chemical formula (2), a and b are set to satisfy the followinginequality expressions: 0.05≤a≤0.3, and 0.05≤b<0.3. Thus, the brightnessof the emitted red light can be improved. Examples of MGF phosphors aredisclosed by Japanese Patent Application No. 2014-113515, JapanesePatent Application No. 2015-96952 and U.S. patent application Ser. No.14/724,118, filed by the applicant of the present application. Theentire contents of Japanese Patent Application No. 2014-113515, JapanesePatent Application No. 2015-96952 and U.S. patent application Ser. No.14/724,118 are incorporated herein by reference.

One embodiment of a method of manufacturing a MGF phosphor in theembodiment of the present invention will be described below. First, MgO,MgF₂, Sc₂O₃, GeO₂, Ga₂O₃, and MnCO₃ are weighed as raw materials toattain the desired composition ratio. After mixing these raw materialstogether, the mixture is charged into a cruicible and calcined at atemperature of 1000 to 1300° C. under atmosphere, thus producing a MGFphosphor. The ratio of the emission intensity at the peak wavelength ofthe light emitting element to the emission intensity at the peakwavelength the red phosphor is preferably 100:55 to 70 (i.e. thefirst:the second=100:55 to 70).

3) Green Quantum Dot

The green quantum dots 24 may be nano-sized particles of a semiconductormaterial. Examples thereof include a group II-VI, a group III-V, and agroup IV-VI compound semiconductor nano-sized particles, morespecifically, a nano-sized particles made of CdSe, a core-shellCdSxSe_(1−x)/ZnS, and GaP. The green quantum dots 24 may have a particlesize (average particle size), for example, of 1 to 20 nm. The greenquantum dots 24 emit green light having a wavelength of the emissionpeak of e.g., 510 to 560 nm. A full width at half maximum of theemission peak wavelength of the green quantum dots 24 is small, namely40 nm or less, and preferably 30 nm or less. The green quantum dots maybe surface-modified or stabilized by a resin and the like, such aspolymethyl methacrylate (PMMA). The term “particle size” as used hereinmeans the particle size of a core part made of semiconductor materialwhich does not contain the resin part or the like which is added forsurface modification and stabilization.

4) Light-Transmissive Material

The light-transmissive material 22 allows the blue light, the greenlight and the red light to pass therethrough. The light-transmissivematerial allows transmittance of preferably 60% or more, more preferably70% or more, still more preferably 80% or more, and most preferably 90%or more of the light emitted from the light emitting element 1 andincident on the light-transmissive material 22. Examples of suitablelight-transmissive material 22 include, high strain point glass, sodaglass (Na₂O.CaO.SiO₂), borosilicate glass (Na₂O.B₂O₃.SiO₂), forsterote(2MgO.SiO₂), lead glass (Na₂O.PbO.SiO₂), and alkali-free glass. Examplesof suitable light-transmissive material 22 also include organic polymers(that may take the forms of polymer material, such as a plastic film, aplastic sheet, and a plastic substrate, each of which is made of apolymer material and has flexibility), the examples include, apolymethyl methacrylate (PMMA), a polyvinyl alcohol (PVA), a polyvinylphenol (PVP), a polyethersulfone (PES), a polyimide, a polycarbonate(PC), a polyethylene terephthalate (PET), a polystyrene (PS), apolyethylene naphthalate (PEN), a cyclic amorphous polyolefin, amultifunctional acrylate, a multifunctional polyolefin, an unsaturatedpolyester, an epoxy resin and a silicone resin.

5) Sealing Resin

The sealing resin 12 allows the blue light and the red light to passtherethrough, and preferably also allows the green light to passtherethrough. The sealing resin 12 allows transmittance of preferably60% or more, more preferably 70% or more, still more preferably 80% ormore, and most preferably 90% or more of the light emitted from thelight emitting element 1 and incident on the sealing resin 12. Examplesof suitable materials for the sealing resin 12 include, a siliconeresin, a modified silicone resin, an epoxy resin, a modified epoxyresin, a phenol resin, a polycarbonate resin, an acrylic resin, a TPXresin, a polynorbornene resin, or a hybrid resin containing one or moreof these resins. Of these resins, the silicone resin is preferablebecause of its good resistance to light and heat. The epoxy resin isalso a preferable resin.

6) Resin Package

The resin package 3 may be formed of any suitable resin. Examples ofpreferable resins include, a thermoplastic resin containing at least oneof an aromatic polyamide resin, a polyester resin, and a liquid crystalresin; or a thermosetting resin containing at least one of an epoxyresin, a modified epoxy resin, a phenol resin, a silicone resin, amodified silicone resin, a hybrid resin, an acrylate resin, an urethaneresin. The resin package 3 is preferably formed of a white resin. Thisis because of the light propagating through the sealing resin 12, moreof the light reaching the resin package 3 can be reflected.

2. Second Embodiment

FIG. 5 shows a schematic cross-sectional view of a light emitting device100A according to a second embodiment. In the above-mentioned lightemitting device 100, the sealing resin 12 contains particles of a redphosphor 14. Meanwhile, in the light emitting device 100A, in place ofthe sealing resin 12 to contain the red phosphor particles 14, thelight-transmissive material 22 contains the red phosphor particles 14.Thus, the red phosphor particles 14 and the green quantum dots 24 aredisposed in the light-transmissive material 22, accordingly, the redphosphor particles 14 and the green quantum dots 24 are positioned atsubstantially the same distance with respect to the light emittingelement 1.

The light emitting element package 10A may have substantially similarstructure as that of the light emitting element package 10 in the firstembodiment except that the sealing resin 12 does not contain the redphosphor particles 14. A green quantum dot-containing layer 20A may havesubstantially similar structure as that of the green quantumdot-containing layer 20 in the first embodiment except that it containsnot only the green quantum dots 24 but also the red phosphor particles14.

As described above, in the light emitting device 100 of the firstembodiment, with respect to the light emitting element 1, the redphosphor particles 14 are positioned closer than the green quantum dots24, while in the light emitting device 100A of the second embodiment,the red phosphor particles 14 and the green quantum dots 24 arepositioned substantially at the same distance with respect to the lightemitting element 1. The respective embodiments have differentadvantages. These advantages will be described below.

1) Advantages of Light Emitting Device 100

FIGS. 6A and 6B are schematic cross-sectional views for illustrating theadvantages of the light emitting devices 100 and 100A. FIG. 6A is aschematic cross-sectional view showing the embodiment of the redphosphor particles 14 disposed in the sealing resin 12. FIG. 6B is aschematic cross-sectional view showing another embodiment of the redphosphor particles 14 disposed in the light-transmissive material 22. Asdescribed above, the red phosphor 14 has a particle size of 20 to 50 μm,while the green quantum dots 24 have a particle size of 2 to 10 nm.These particle sizes differ significantly from each other, morespecifically, the former is about three to four orders of magnitudegreater than the latter.

FIGS. 6A and 6B are schematic diagrams illustrated for the purpose ofclarifying the advantages of the light emitting devices 100 and 100A dueto the difference in the particle sizes. In comparison with FIGS. 1 and5 , FIGS. 6A and 6B more clearly show the difference in the particlesize between the red phosphor particles 14 and the green quantum dots24.

Reference numeral 114 in FIG. 6A schematically represents red light(part of red light) emitted from a red phosphor particle 14X, which isone of a plurality of red phosphor particles 14, and reference numeral124 schematically represents green light (part of green light) emittedfrom a green quantum dot 24X, which is one of a plurality of greenquantum dots 24. Likewise, reference numeral 114A in FIG. 6Bschematically represents red light (part of red light) emitted from ared phosphor particle 14Y, which is one of a plurality of red phosphorparticles 14, and reference numeral 124A schematically represents greenlight (part of green light) emitted from a green quantum dot 24Y, whichis one of a plurality of green quantum dots 24.

As shown in FIG. 6B, in the case where the red phosphor particles 14having larger particle size are disposed in the light-transmissivematerial 22, the green light 124A emitted from the green quantum dots24Y is scattered by the red phosphor particles 14 present in the path ofthe green light, and as a result, does not reach the upper surface ofthe green quantum dot-containing layer 20A (in FIG. 6B, the red light114A exits from the upper surface of the green quantum dot-containinglayer 20A to the outside, while the green light 124A does not reach theupper surface of the green quantum dot-containing layer 20A). Thepresence of the red phosphor particles 14 having a large particle sizein the green quantum dot-containing layer 20A causes such scattering ofa portion of the green light, which might slightly reduce the luminousefficiency.

On the other hand, as shown in FIG. 6A, the green quantum dot-containinglayer 20 does not contain the red phosphor particles 14 having a largeparticle size, and contains only the green quantum dots 24 except forthe light-transmissive material 22. The green light propagating throughthe green quantum dot-containing layer 20 is much less likely to bescattered by the green quantum dots 24 having a very small particle size(in FIG. 6A, the red light 114 and the green light 124 exit to theoutside from the upper surface of the green quantum dot-containing layer20). Thus, the higher luminous efficiency can be obtained.

2) Advantages of Light Emitting Device 100A

The green quantum dot-containing layer 20A of the light emitting device100A contains both the red phosphor particles 14 and the green quantumdots 24 as described above. Although the red phosphor particles 14 haveless thermal degradation compared to the green quantum dots 24, such anarrangement can suppress the transfer of heat generated from the lightemitting element 1 to the red phosphor particles 14, accordingly,degradation of the red phosphor particles 14 can be more reliablysuppressed.

Moreover, the red phosphor particles 14 and the green quantum dots 24are arranged in the light-transmissive material 22, so that thewavelength converting material has to be disposed only in thelight-transmissive material 22, and the red phosphor particles 14 arenot needed to be disposed in the sealing resin 12. Accordingly, themanufacturing procedure can be simplified.

As described above, in the light emitting device 100A, thelight-transmissive material 22 of the green quantum dot-containing layer20A contains the red phosphor particles 14, and the sealing resin 12 ofthe light emitting element package 10A does not contain the red phosphorparticles 14. But alternatively, both the light-transmissive material 22of the green quantum dot-containing layer 20A and the sealing resin 12of the light emitting element package 10A may contain the red phosphorparticles 14.

3. Third Embodiment

FIG. 7 is a schematic cross-sectional view showing a liquid crystaldisplay device 200 that has a light emitting device 100B according to athird embodiment. The light emitting device 100B includes the lightemitting element package 10, the green quantum dot-containing layer 20,and a light guide plate 52 disposed between the light emitting elementpackage 10 and the green quantum dot-containing layer 20. In theembodiment shown in FIG. 7 , the light guide plate 52 is disposedbetween the sealing resin 12 of the light emitting element package 10and the green quantum dot-containing layer 20. More specifically, thesealing resin 12 is arranged facing one side surface of the light guideplate 52, and the green quantum dot-containing layer 20 is disposedfacing the upper surface of the light guide plate 52. In the embodimentshown in FIG. 7 , the light emitting element package 10 is of a top-viewtype, but is not limited thereto, and may have any other form, such asthe side-view type mentioned above.

The light emitting device 100B may include a reflecting plate(reflector) 51 on the lower surface of the light guide plate 52 toupwardly reflect a portion of the light entering the light guide plate52 through the light emitting element package 10 and reaching the lowersurface of the light guide plate 52, and then to direct the reflectedlight toward the upper surface of the light guide plate 52.

In the embodiment shown in FIG. 7 , the light emitting element package10 is disposed spaced apart from the light guide plate 52, but is notlimited thereto. The light emitting element package 10 and the lightguide plate 52 may be arranged in contact with each other by, forexample, arranging the sealing resin 12 or the resin package 3 incontact with the side surface of the light guide plate 52. The greenquantum dot-containing layer 20 may be arranged in contact with theupper surface of the light guide plate 52, or spaced apart from thelight guide plate 52.

A lower polarizing film 53A is disposed on the green quantumdot-containing layer 20. A liquid crystal cell 54 is disposed on thelower polarizing film 53A, and a color filter array 55 is disposed onthe liquid crystal cell 54. The color filter array 55 includes aplurality of color filter portions corresponding to different colors,each filter portion allowing only the light of a specific color to passtherethrough. The color filter portions include, for example, red colorfilter portions 55A, green color filter portions 55B and blue colorfilter portions 55C. An upper polarizing film 53B is disposed on thecolor filter array 55.

Next, the operation of the liquid crystal display device 200 will bedescribed.

A portion of blue light emitted from the light emitting element 1 exitsfrom the sealing resin 12. Another portion of the blue light emittedfrom the light emitting element 1 is absorbed in the red phosphorparticles 14 disposed in the sealing resin 12, and then red light isemitted from the red phosphor particles 14. The red light emitted fromthe red phosphor particles 14 exits through the sealing resin 12. Thatis, a purple light, which is a mixture of the blue light and the redlight, is emitted from the light emitting element package 10. The purplelight (blue light+red light) enters the green quantum dot-containinglayer 20 via the light guide plate 52. A portion of the blue lightentering the green quantum dot-containing layer 20 is absorbed in thegreen quantum dots 24, whereby the green quantum dots 24 emit a greenlight. As a result, a white light which is a mixture of the blue light,the green light, and the red light is emitted from the upper surface ofthe green quantum dot-containing layer 20. The white light enters thelower polarizing film 53A. A portion of the white light (bluelight+green light+red light) entering the lower polarizing film 53Apasses through the lower polarizing film 53A to enter the liquid crystalcell 54. A portion of the white light entering the liquid crystal cell54 passes through the liquid crystal cell 54 to reach the color filterarray 55.

The blue light, the green light and the red light reaching the colorfilter array 55 can pass through the corresponding filter portion. Forexample, the red light passes through the red color filter portions 55A,the green light passes through the green color filter portions 55B, andthe blue light passes through the blue color filter portions 55C. Eachof the blue, green and red lights passing through the color filter array55 can partially pass through the upper polarizing film 53B. In thisway, the liquid crystal display device 200 can display a desired image.

As described above, each of the red light emitted from the red phosphor14 and the green light emitted from the green quantum dots 24 has anarrow full width at half maximum of the emission peak, and thus has thehigh color purity. Also, larger amount of light can pass through the redcolor filter portions 55A and the green color filter portions 55B, sothat the luminous efficiency can be improved.

Although the disclosure has been described with reference to severalexemplary embodiments, it shall be understood that the words that havebeen used are words of description and illustration, rather than wordsof limitation. Changes may be made within the purview of the appendedclaims, as presently stated and as amended, without departing from thescope and spirit of the disclosure in its aspects. Although thedisclosure has been described with reference to particular examples,means, and embodiments, the disclosure may be not intended to be limitedto the particulars disclosed; rather the disclosure extends to allfunctionally equivalent structures, methods, and uses such as are withinthe scope of the appended claims.

The illustrations of the examples and embodiments described herein areintended to provide a general understanding of the various embodiments,and many other examples and embodiments may be apparent to those ofskill in the art upon reviewing the disclosure. Other embodiments may beutilized and derived from the disclosure, such that structural andlogical substitutions and changes may be made without departing from thescope of the disclosure. Additionally, the illustrations are merelyrepresentational and may not be drawn to scale. Certain proportionswithin the illustrations may be exaggerated, while other proportions maybe minimized. Accordingly, the disclosure and the figures are to beregarded as illustrative rather than restrictive.

One or more examples or embodiments of the disclosure may be referred toherein, individually and/or collectively, by the term “disclosure”merely for convenience and without intending to voluntarily limit thescope of this application to any particular disclosure or inventiveconcept. Moreover, although specific examples and embodiments have beenillustrated and described herein, it should be appreciated that anysubsequent arrangement designed to achieve the same or similar purposemay be substituted for the specific examples or embodiments shown. Thisdisclosure may be intended to cover any and all subsequent adaptationsor variations of various examples and embodiments. Combinations of theabove examples and embodiments, and other examples and embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the description.

In addition, in the foregoing Detailed Description, various features maybe grouped together or described in a single embodiment for the purposeof streamlining the disclosure. This disclosure may be not to beinterpreted as reflecting an intention that the claimed embodimentsrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter may bedirected to less than all of the features of any of the disclosedembodiments. Thus, the following claims are incorporated into theDetailed Description, with each claim standing on its own as definingseparately claimed subject matter.

The above disclosed subject matter shall be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments which fall within thetrue spirit and scope of the present disclosure. Thus, to the maximumextent allowed by law, the scope of the present disclosure may bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description.

All of the publications, patent applications and patents cited hereinare incorporated herein by reference in their entirety.

What is claimed is:
 1. A light emitting device, comprising: a lightemitting element adapted to emit blue light; a sealing resin coveringthe light emitting element; a phosphor included in the sealing resin andadapted to absorb a portion of the blue light emitted from the lightemitting element to emit red light; and a quantum dot layer disposedoutside the sealing resin, the quantum dot layer including quantum dotsadapted to absorb a portion of the blue light emitted from the lightemitting element to emit green light having an emission peak wavelengthof 510 nm to 560 nm, wherein the phosphor has a half-width of anemission peak of 35 nm or less, wherein the quantum dots have an averageparticle size of 1 nm to 20 nm, wherein the quantum dot layer issheet-shaped and is spaced apart from the sealing resin, and wherein alight guide plate is disposed between the sealing resin and the quantumdot layer.
 2. The light emitting device according to claim 1, whereinthe sealing resin is disposed facing one side surface of the light guideplate, and the quantum dot layer is disposed facing an upper surface ofthe light guide plate.
 3. The light emitting device according to claim1, wherein the sealing resin further includes fillers.
 4. The lightemitting device according to claim 1, wherein the light emitting elementand the sealing resin constitute a part of a light emitting elementpackage and wherein chromaticity of light emitted from the lightemitting element package is in a quadrangular region formed byconnecting four points of (0.4066, 0.1532), (0.3858, 0.1848), (0.1866,0.0983) and (0.1706, 0.0157) on xy chromaticity coordinate system ofCIE1931 chromaticity diagram.
 5. The light emitting device according toclaim 1, wherein the light emitting element and the sealing resinconstitute a part of a light emitting element package and whereinchromaticity of light emitted from the light emitting element package isin a quadrangular region formed by connecting four points of (0.19,0.099779), (0.19, 0.027013), (0.3, 0.09111) and (0.3, 0.14753) on xychromaticity coordinate system of CIE1931 chromaticity diagram.
 6. Thelight emitting device according to claim 1, wherein the phosphorincludes a MGF phosphor or is a combination of a KSF phosphor and theMGF phosphor, the KSF phosphor being adapted to absorb a portion of theblue light emitted from the light emitting element to emit red light,and the MGF phosphor being adapted to absorb a portion of the blue lightemitted from the light emitting element to emit red light and whereinthe KSF phosphor is a compound having the chemical formula:A₂[M_(1-a)Mn⁴⁺ _(a)F₆]  (1) where A is at least one selected from thegroup consisting of K⁺, Na⁺, Rb⁺, Cs⁺, and NH₄ ⁺, M is at least oneelement selected from the group consisting of Group 4 elements and Group14 elements, and 0<a<0.2; wherein the MGF phosphor is a compound havingthe chemical formula:(x−a)MgO.(a/2)Sc₂O₃ .yMgF₂ .cCaF₂.(1−b)GeO₂.(b/2)Mt₂O₃ :zMn⁴⁺  (2) where2.0≤x≤4.0, 0<y<1.5, 0<z<0.05, 0≤a<0.5, 0<b<0.5, 0≤c<1.5, y+c<1.5, and Mtis at least one element selected from Al, Ga and In.
 7. The lightemitting device according to claim 6, wherein the KSF phosphor or theMGF phosphor have a particle size of 20 μm to 50 μm.
 8. The lightemitting device according to claim 6, wherein the sealing resin includesthe KSF phosphor.
 9. The light emitting device according to claim 6,wherein the KSF phosphor is disposed in the quantum dot layer.
 10. Thelight emitting device according to claim 1, wherein the quantum dotshave an average particle size of 2 nm to 10 nm.
 11. The light emittingdevice according to claim 1, wherein a full width at half maximum of theemission peak wavelength of the quantum dots adapted to absorb a portionof the blue light emitted from the light emitting element to emit greenlight is 40 nm or less.
 12. The light emitting device according to claim1, wherein a full width at half maximum of the emission peak wavelengthof the quantum dots adapted to absorb a portion of the blue lightemitted from the light emitting element to emit green light is 35 nm orless.